1. Field
Example embodiments of the inventive concepts relate to a memory device using flag cells and a system including the memory device.
2. Description of the Related Art
Examples of nonvolatile memories using resistance materials include phase-change random access memories (PRAMs) or phase-change memories (PCMs), resistive RAMs (RRAMs), and magnetic RAMs (MRAMs). While dynamic RAMs (DRAMs) or flash memories store data using charges, nonvolatile memories using resistance materials store data using a state change of a phase-change material such as chalcogenide alloy (in the case of PRAMs), a resistance change of a variable resistance material (in the case of RRAMs), or a resistance change of a magnetic tunnel junction (MTJ) thin film according to a magnetization state of a ferromagnetic material (in the case of MRAMs).
In particular, a phase-change material of a PRAM or PCM may become a crystalline state or an amorphous state as it is cooled after being heated by a write current. The phase-change material has low resistance in the crystalline state and has high resistance in the amorphous state. Therefore, the crystalline state may be defined as set data or data 0, and the amorphous state may be defined as reset data or data 1.
In a PRAM, the resistance of a phase-change material may drift for a predetermined or reference period of time (referred to as a stabilization time) even after a predetermined or reference resistance (set data or reset data) is programmed into the phase-change material. That is, the resistance of the phase-change material may gradually increase during the stabilization time but may hardly change after the stabilization time. Therefore, if a programmed PRAM cell is read during the stabilization time, wrong data may be read, resulting in a read error.